Equip a two-handed weapon together with a shield:

1. Equip a shield, leave your main hand empty
2. Select a spell instead of melee attack as your action
3. Equip a two-handed weapon onto your main hand

Equip a two-handed weapon together with a single-hand weapon:

1. Equip two single-hand weapon onto both hands
2. Select a spell instead of melee attack as your action
3. Remove the single-hand weapon from your main hand, then equip a two-handed weapon onto the main hand

Enjoy!